This invention pertains to a means for maintaining the security of a substrate, and in particular a means for maintaining the security of banknotes or financial documents.
Known in the state of the art are means for maintaining security formed by narrow strips presenting an easily recognizable and verifiable visual appearance and limiting the risks of counterfeiting.
As an example, EP 229645 describes a process for creating a security paper comprising a security element incorporated in the paper in the form of a thread or a strip. The security element is situated at least locally in the thinnest regions of the paper or on the surface of the paper.
A first paper layer is formed by a first wet part of a paper machine, which is detached from the metal netting by means of a gripper band. A second layer of paper is formed on a second wet part of a paper machine. One or both of the two layers of paper have at least local regions that are thinner, representing up to 30% of the total thickness of the two layers of paper.
In order to improve this process of the prior art, U.S. Pat. No. 4,943,093 proposes creation of a security paper and a security device placed between the two surfaces of the paper as a characteristic of public security, comprising a flexible substrate with a metal layer on one surface of the substrate. The security device, which has a width smaller than 5 mm, is positioned at least partially between the surfaces of the paper. A continuous metallic track is present on at least one side of the device along its entire length. The device has demetallized parts which are permeable to light and which comprise between 10 and 50% of the surface of the device. The parts without metal placed along the length of the device form a pattern, a design or repetitive marks.
It would therefore be advantageous to further reinforce the security of such solutions by providing a security means that is easy to implement and difficult to counterfeit.
This invention relates to an apparatus for maintaining security of a substrate having an optically verifiable mark including a partially demetallized metallic layer which forms a control graphic, a layer of optically active pigments adjacent the metallic layer, and an adhesive layer adjacent the layer of optically active pigments.